The present invention applies to gas turbine engines and, more particularly, to a thrust reverser for use with an asymmetric aircraft gas turbine engine exhaust nozzle. The invention is particularly adaptable to twin engine, high performance combat aircraft which are provided with such asymmetric exhaust nozzles.
It is important in modern, high performance fighter aircraft that means be provided for suddenly arresting or decreasing the flight speed in order to enhance maneuvering capability under combat conditions. It is also important that such combat aircraft be provided with means for reducing the length of the aircraft landing roll in order to permit landing on short runways. Even commercial aircraft requires some means for augmenting conventional braking in order to arrest the speed of the aircraft after landing.
The traditional and most efficient means for accomplishing these functions has been, and will continue to be, a thrust reverser attached to or incorporated within the gas turbine engine exhaust nozzle. Such reversers have applicability only to engines of the gas turbine variety (commonly referred to as "jet engines") since recirpocating engines may more readily be provided with variable pitch propellers which can effect thrust reversal through rotation of each propeller blade about its longitudinal axis. While much progress is being made in adapting variable pitch mechanisms to gas turbine engines of the high bypass variety, of which U.S. Pat. No. 3,994,128, entitled "Dual Output Variable Pitch Turbofan Actuation System," Griswold et al, is an excellent proven example, conventional thrust reversers will continue to be the means for reversing thrust in gas turbine engines of the turbojet or low bypass ratio turbofan type characteristic of modern high performance fighter aircraft. These devices, when deployed, redirect the exhaust gas in the forward direction, thus reversing the thrust vector.
However, a new family of gas turbine exhaust nozzles is emerging which offers improved installed performance characteristics over the former exhaust nozzles which are characterized as being axisymmetric. Traditionally, these nozzles are cylindrical, frustoconical, or a combination of the two geometries which produces a nozzle which is symmetric about a central longitudinal axis. The new family of nozzles, typified by the proven augmented deflecting exhaust nozzle of U.S. Pat. No. 4,000,610, entitled "Flight Maneuverable Nozzle for Gas Turbine Engines," Nash et al, and assigned to the assignee of the present invention, is characterized as being asymmetric as a result of careful attention being paid to the integrated effects of engine and airframe performance, and also as a result of a recognition of the necessity for enhancing aircraft maneuverability through in-flight exhaust vectoring. The augmented deflecting exhaust nozzle (ADEN) of U.S. Pat. No. 4,000,610, being primarily adapted to high performance combat aircraft, will also strongly benefit through the provision of a reverse thrust capability. The ADEN, however, being an asymmetric exhaust nozzle, is difficult to fit with a conventional thrust reverser, particularly in a twin engine, side-by-side installation. The reverse exhaust flow from each engine must, in twin engine installations, be ejected in the vertical plane due to the presence of the laterally adjacent engine, and the ADEN is not symmetrical in the vertical plane. Furthermore, prior art thrust reversers have been designed for use with traditional axisymmetric nozzles with little attention being given to their integration into an in-flight maneuvering enhancement nozzle.
The problem is that in order to produce reverse thrust without an accompanying pitch movement, which could create aircraft instability, it is necessary that the reversed exhaust stream be split into two streams, one of which is deflected upward and forward by more than 90.degree. and the other of which is deflected downward and forward by more than 90.degree., with the unavoidable transverse components of thrust being equal and opposite to cancel any adverse effect on aircraft attitude control. In other words, the reverse exhaust flow must be arranged so that only pure reverse thrust is created without extraneous transverse force components or pitching moments. The present invention provides a means for effectively reversing the thrust in asymmetric nozzles such as the in-flight maneuvering ADEN without degradation to its clearly superior installed performance characteristics. In fact, incorporation of the subject invention into the ADEN will even further enhance the in-flight maneuvering capability of any aircraft in which it is installed.